1. Field
One embodiment of the invention relates to an apparatus and method for receiving video data via a digital interface.
2. Description of the Related Art
An example of a multimedia interface between a video-data transmission apparatus, such as a DVD player, a digital tuner and a set-top box, and a video data-data receiver apparatus, such as a TV receiver and a monitor, is one complying with the high definition multimedia interface (HDMI) standard (High-Definition Multimedia Interface Specification Version 1.3a). Any apparatus that has an HDMI output terminal is called a source apparatus, and any apparatus that has an HDMI input terminal is called a sink apparatus. The video-data transmission apparatus is a source apparatus, while the video data-data receiver apparatus is a sink apparatus. Any apparatus that has an HDMI input terminal and an HDMI output terminal and performs both the function of a source apparatus and the function of a sink apparatus is known as a repeater apparatus.
When the source apparatus is connected to the sink apparatus, the source apparatus transmits a +5V power-supply signal to the sink apparatus, informing the sink apparatus that the source apparatus has been connected to the sink apparatus. The +5V power-supply signal is also a signal showing that the source apparatus is ready to operate.
Upon receiving the +5V power-supply signal, the sink apparatus starts making itself prepared to receive video data. When so prepared, the sink apparatus transmits a hot-plug detection (HPD) signal (High signal) to the source apparatus. The hot-plug detection (HPD) signal is also a signal showing that the sink apparatus is now ready to receive video data.
The sink apparatus has an EDID memory that stores extended display identification data (EDID), i.e., the video-format data that the sink apparatus can display. The video-format data includes video specification items such as video format, resolution and sync frequency, and audio specification items such as audio-data format, sampling frequency Fs and bit length.
Upon receiving the HPD signal at a high level, the source apparatus reads the EDID from the EDID memory of the sink apparatus through a display-data channel (DDC) line, reading the video-format data, which is written in the EDID and in which the sink apparatus can display video data.
The source apparatus transmits and receives data required to achieve the authentication of high-bandwidth digital content protection (HDCP), to and from the sink apparatus through the DDC line. The data required to achieve the authentication is, for example, HDCP key data. In this instance, the HDCP key data is assumed to be stored in a storage area the sink apparatus has. For the source apparatus, to authenticate the high-bandwidth digital content protection is to confirm that the sink apparatus is authorized to receive video signals. Upon authenticating the high-bandwidth digital content protection, the source apparatus decrypts the video data with the secret-key data shared with the sink apparatus, and then transmits the video data, thus decrypted, to the sink apparatus.
After reading and authenticating the EDID, the source apparatus transmits video data, audio data and AUX data, all complying to the sink-apparatus format, to the sink apparatus by means of transmission minimized differential signaling (TMDS).
The HDMI standards describe optional standards concerning the mutual control of apparatuses, known as consumer electronic control (CEC). HDMI devices are tree-connected by repeaters. The CEC utilizes a single-line, low-speed serial bus. One of the functions the CEC achieves is a one-touch display in which the source apparatus controls the sink apparatus. When the source apparatus (e.g., a DVD player) is set to the playback mode (that is, when the playback button on the apparatus is pushed), the source apparatus controls the sink apparatus (e.g., a TV receiver) and to automatically turns on the sink apparatus if necessary and automatically connect the signal path to it (i.e., DVD player). Thus, the source apparatus enables the sink apparatus to display the image played back.
In order to designate one of apparatuses so that a switching device may be controlled to set a signal path, all apparatuses must have a physical address each. The physical address of the source apparatus is written in the EDID of the sink apparatus or the EDID of the repeater apparatus. When the apparatuses are mutually tree-connected anew or disconnected from the tree connection, changing the tree connection, physical addresses are detected. Thus, the physical addresses of all sink apparatuses and all repeater apparatuses are detected and propagated. If the tree connection is composed of five stages at most, the address of each apparatus is a four-digit data item, represented as “n.n.n.n.” Any sink apparatus or repeater apparatus that serves as a route, generates its physical address “0.0.0.0.” The sink apparatus or repeater apparatus reads its physical address from the EDID memory of the sink apparatus connected to it.
The timing the source apparatus or repeater apparatus reads its own physical address is the time when it receives the high-level HPD signal that the sink apparatus or repeater apparatus transmits in response to the +5V power-supply signal it receives from the source apparatus. The sink apparatus has a plurality of HDMI ports, but only one EDID memory. Hence, the source apparatus or repeater apparatus may fail to read its own physical address, depending on whether or not power is supplied to the source, sink and repeater apparatuses and whether or not the switching device has set a signal path for any apparatus designated.
Assume that a source apparatus #1 is connected to a port #1 of a sink apparatus (thus, the port #1 is selected). In this case, the source apparatus #1 acquires physical address “1.0.0.0” when the HPD signal rises to a high level. The source apparatus #1 holds this physical address even after the HPD signal falls back to a low level. If the source apparatus is pulled out of the port #1, the sink apparatus cannot detect this event because the HPD signal is now at a low level. The HPD signal remains low even if the source apparatus #1 is connected to a port #2, because the port #2 is not selected. Consequently, the source apparatus #1 keeps holding the physical address of the port #1, and cannot acquire the correct physical address “2.0.0.0.” Therefore, correct CEC control may not be performed.
Thus, any apparatus that receives video data from a data transmission apparatus through a conventional digital interface, e.g., HDMI, must exchange physical addresses with the data transmission apparatus so that the data receiver apparatus and the data transmission apparatus may control each other. However, the data transmission apparatus may fail to read the physical address of the data receiver apparatus, depending on what state the apparatuses assume and which apparatus the switching device selects.